How should I reduce the ammonia and nitrites in my tank water?

With a properly cycled aquarium, you should never see any detectable ammonia or nitrites.

If your tank has cycled properly and you now have ammonia or nitrites in your water, you need to first detoxify and/or lower the concentration, then figure out why it’s there.

Some water conditioners can detoxify ammonia and nitrite in addition to remove chloramines. Standard tap water conditioners use sodium thiosulfate to convert the chlorine component of chloramine to chloride. This results in a small amount of free ammonia in the water. Seachem Prime, Tetra AquaSafe NH/CL Formula, Jungle's ACE, Kordon AmQuel, and Kent Professional Ammonia Detox can convert the resulting ammonia into non-toxic ammonium. This will keep your fish from getting ammonia burns while still allowing your biological filter to process the non-toxic ammonium into nitrites. If the water conditioner label doesn't specifically mention that it neutralizes ammonia, then it won't help.

The easiest and fastest way to reduce ammonia and nitrites in the short term is to do a large water change. A 50% water change will dilute the concentration of toxins in your aquarium by roughly 1/2. You should test for ammonia and nitrites after the water change. Your goal is to reduce the levels to 1 ppm or less. Do additional water changes if necessary to get to this level. You may need to temporarily test your water and/or do water changes 2-3 times per week to keep the concentration down until the underlying problem is solved.

There are several factors that can contribute to ammonia and nitrite spikes. Power outages cause your filters to stop working. Over time, your bacteria colony will die off due to a lack of oxygenated water and food. Adding several new fish to your tank can cause a “mini-cycle” while your bio filter increases its capacity to deal with the additional load. Inadequate filtration can cause high readings because the filter cannot keep up with the bio load of your fish.

If you have an extended power outage, and you see ammonia or nitrite spikes, your tank may need to start the cycle over again. It may take less time than the first cycle because some bacteria may still live in your substrate and aquarium surfaces. To decrease cycle times, you can add filter media from other established tanks. During this period you should use frequent water changes to keep ammonia and nitrites below 1 ppm.

If you recently added fish to your tank, then your tank has probably started a “mini-cycle” as mentioned above. If so, you should do a large water change to reduce the ammonia and nitrites. Over several days, your biological filter will increase in capacity to deal with the added load. Continue to monitor your ammonia and nitrite readings for increases until you’re sure the filter has stabilized.

If power outages or new fish aren’t the cause of increased ammonia and nitrites, then inadequate filtration may be the cause. As a general rule, you want a lot of filtration on an oscar tank. You should not use a filter’s stated capacity as the only method to determine your filtration needs. You wouldn’t want to stock a 125 gallon tank with two oscars and a pleco and filter it with 1 Aquaclear 500. That tank size is within the filter’s stated capacity of 150 gallons, but that in reality that is an extremely underfiltered tank. If you’re unsure about your needs, post a message to the board detailing your tank, fish including size, and current filtration. We should be able to determine fairly quickly if filtration capacity is an issue.